首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   7002篇
  免费   8篇
  国内免费   1篇
电工技术   7篇
综合类   6篇
化学工业   105篇
金属工艺   4篇
机械仪表   8篇
建筑科学   36篇
矿业工程   3篇
能源动力   17篇
轻工业   56篇
水利工程   10篇
石油天然气   2篇
无线电   98篇
一般工业技术   121篇
冶金工业   6432篇
原子能技术   4篇
自动化技术   102篇
  2021年   7篇
  2019年   6篇
  2017年   3篇
  2016年   9篇
  2015年   4篇
  2013年   33篇
  2012年   20篇
  2011年   22篇
  2010年   19篇
  2009年   16篇
  2008年   18篇
  2007年   23篇
  2006年   17篇
  2005年   22篇
  2004年   12篇
  2003年   38篇
  2002年   21篇
  2001年   13篇
  2000年   17篇
  1999年   226篇
  1998年   2059篇
  1997年   1121篇
  1996年   818篇
  1995年   431篇
  1994年   352篇
  1993年   394篇
  1992年   51篇
  1991年   96篇
  1990年   55篇
  1989年   74篇
  1988年   65篇
  1987年   69篇
  1986年   73篇
  1985年   59篇
  1984年   8篇
  1983年   10篇
  1982年   34篇
  1981年   47篇
  1980年   75篇
  1979年   17篇
  1978年   21篇
  1977年   146篇
  1976年   323篇
  1975年   16篇
  1974年   5篇
  1973年   9篇
  1972年   7篇
  1971年   4篇
  1970年   4篇
  1955年   5篇
排序方式: 共有7011条查询结果,搜索用时 15 毫秒
101.
BACKGROUND/PURPOSE: The development of thoracoscopic surgery has made many procedures possible, including the treatment of mediastinal cysts in children. The authors report their experience with this procedure between 1992 and 1997. METHODS: Surgery was performed on 22 children aged from 1 month to 9 years (median, 27 months), weighing 5 to 49 kg (median, 12.5 kg). Diagnosis was made by antenatal ultrasound scan in six cases (27%), with a chest x-ray performed for respiratory symptoms in 14 cases, and with a chest x-ray performed for positive tuberculin intradermoreaction in two cases. Decision to resect the cyst was determined by thoracoscopy in 21 of the 22 cases, and by open surgery in one case only (subcarinal compressive cyst with left lung distension and a mediastinal shift). RESULTS: Eighteen of the 21 (86%) cases were treated successfully by thoracoscopy. In three cases of bronchogenic cysts, we performed an associated thoracotomy because the dissection was too difficult and dangerous. In three cases, a small part of a common wall between the cyst and the bronchus was not removed. The pathological diagnosis was bronchogenic cysts in 15 cases (71%), pleuropericardiat cysts in three cases (14%), esophageal duplication in two cases (10%), and cystic hygroma in one case (5%). Two postoperative complications were observed: one esophageal wound and a case of recurrent pneumothorax after chest tube removal. Patients were discharged after 2 to 11 days (median, 3 days). Follow-up was uneventful. CONCLUSIONS: Treatment of mediastinal cyst by thoracoscopy is feasible in most cases. Compressive cysts with lung distension and mediastinal shift remain a contraindication. If the cysts have a common wall with the bronchus or esophagus, or if they are subcarinal, the dissection may be difficult and dangerous, and thoracotomy may be preferable.  相似文献   
102.
BACKGROUND: Nightshade plants (Solanaceae) have been utilized as hallucinogenic drugs since antiquity in nearly every culture. The Solanaceae alkaloids, atropine and scopolamine, were the active substances in ointment of witches and medieval anesthetics, and in modern poisons. They are still currently used as hallucinogenic drugs. In poisonings, a dosage- and substance-dependent clinical picture occurs, with central and peripheral symptoms. Hallucinations are predominant in the middle dose range, which explains the drugs' earlier utilization for religious and prophetic purposes. Respiratory depression and arrest at high doses confirm the use of scopolamine as a lethal poison. Despite this, the nightshade alkaloids were utilized in clinical medicine in the 19th century. This is an overview of the cultural history of the nightshade alkaloids.  相似文献   
103.
PURPOSE: To evaluate the effectiveness, predictability, and safety of clear lens extraction to correct extreme myopia. SETTING: Clinica de Nuestra Se?ora de la Concepción, Fundación Jiménez Díaz, Madrid, Spain. METHODS: This retrospective study comprised 26 eyes of 17 highly myopic patients who had clear lens extraction and implantation of a negative-power posterior chamber intraocular lens (IOL). The IOL power was calculated using the SRK/T formula. Analyzed were visual and refractive results and intraoperative and postoperative complications. Follow-up was at least 12 months in all cases. RESULTS: Uncorrected visual acuity improved in all cases, with 80.77% of eyes achieving 20/100 or better and 42.30%, 20/40 or better. Best spectacle-corrected visual acuity (BSCVA) improved in 23 eyes (88.46%). The percentage of eyes achieving a BSCVA of 20/100 or better increased from 73.07% preoperatively to 92.30% postoperatively and the percentage achieving 20/40 or better, from 23.07 to 73.07%. Of the 26 eyes, 76.91% were within 1.00 diopter (D) of refractive error and 96.16% were within 2.00 D. No intraoperative complications occurred. Although postoperatively 3 eyes (11.53%) developed choroidal detachment and 5 (19.23%) had an intraocular pressure greater than 25 mm Hg, all had a favorable outcome. Four eyes (15.38%) developed posterior capsule opacification and had a neodymium:YAG laser posterior capsulotomy 6 months postoperatively. No retinal detachments were observed. CONCLUSION: Clear lens extraction with negative-power IOL implantation using the SRK/T formula had good effectiveness, acceptable predictability, and a low morbidity in eyes with extreme myopia over a short follow-up. A longer follow-up with more cases is needed to assess the safety of the procedure.  相似文献   
104.
An enantioselective synthesis of the (1'S,2'R)-dimethylheptyl cannabinoid side chain has been developed and employed in the synthesis of 11-hydroxy-(1'S,2'R)-dimethylheptyl-delta 8-THC (3). Pharmacology, in vivo and in vitro, indicate (3) to be one of the most potent traditional cannabinoids known.  相似文献   
105.
Delta opioid peptide [D-Ala2,D-leu5]enkephalin (DADLE) can prolong organ preservation and increases myocardial tolerance to ischemia. Our study examined the protective property of DADLE against methamphetamine- (METH) induced dopaminergic terminal damage in the central nervous system. Because the neurotoxicity of METH involves reactive oxygen species, we also examined if DADLE might be an antioxidative agent in vitro. DADLE at 2 and 4 mg/kg (i.p.), given 30 min before each METH administration (5 or 10 mg/kg, i.p., four injections in a day at 2-hr intervals), dose-dependently blocked the METH-induced long-term dopamine transporter loss. The opioid antagonist naltrexone blocked this action of DADLE in both aspects of striata but tends not to affect the effects of DADLE in the nucleus accumbens. DADLE did not alter changes in body temperature induced by METH. The reduction of striatal dopaminergic content and tyrosine hydroxylase activity caused by METH, however, were not blocked by DADLE. In vitro, DADLE was approximately equipotent to glutathione in inhibiting both superoxide anion formation induced by xanthine oxidase and hydroxyl radical formation evoked by ferrous/citrate complex. DADLE was only slightly less potent than glutathione in inhibiting the iron/ascorbate-induced brain lipid peroxidation. These results suggest that DADLE can protect the terminal membranes of dopaminergic neurons against METH-induced insult but not the loss of dopaminergic content and tyrosine hydroxylase activity and that this action of DADLE might involve opioid receptors as well as the sequestration of free radical.  相似文献   
106.
This experiment consisted of the following treatment-breed groups: 1) White crossbred gilts, 2) White crossbred gilts treated with progesterone (200 mg/d in corn oil given on d 2 and 3 after estrus), and 3) Chinese Meishan gilts. Pregnant and nonpregnant gilts (n=3 to 6) from each treatment-breed combination were assigned to be slaughtered on d 10, 11, 12, 13, and 15. At slaughter each uterine horn was flushed with 20 mL of minimal essential medium. Uterine flushings were assayed for total protein, acid phosphatase, uteroferrin, retinol-binding protein, and oxytocin. Uterine flush total protein was increased by progesterone treatment, was unaffected by pregnancy status, and was less in Meishans. Similar patterns were found for retinol binding protein and uteroferrin, except that uteroferrin was greater in pregnant than in nonpregnant gilts. Oxytocin was greater in pregnant than in nonpregnant gilts, was not influenced by progesterone treatment, and was similar in Meishan and in White crossbred gilts. These results indicate that the conceptus does not influence secretion of either total protein or retinol binding protein during pregnancy and that the onset of secretion of these uterine proteins may be controlled by progesterone. The presence of the conceptus is associated with increased uteroferrin and oxytocin production. The decreased secretion of uterine proteins in Meishan gilts may partially explain the slower embryonic development that has been reported for this breed.  相似文献   
107.
Myoclonus may be observed in children with mild or severe epileptic syndromes. Both types are seen at characteristic ages, together with other factors: aetiology, family history, hereditary pattern, effect on psychomotor development and EEG-EMG findings. In children with progressive or degenerative encephalopathies and myoclonus, better known as progressive myoclonic epilepsy, there are also specific clinical data, together with biological and genetic markers which permit identification. The most specific clinical characteristics of each of these clinical pictures are described, as are the complementary tests which permit confirmation of these diagnoses.  相似文献   
108.
109.
Much of what has been written in Australia about the protection of computer programs has been inspired by high profile cases concerning the boundaries of copyright protection. The Australian law firm Clayton Utz says that there has been little discussion about other types of legal protection for computer programs, and as a consequence, other intellectual property laws should not be overlooked.  相似文献   
110.
According to our common medical culture, some facts are simply unquestionable, for instance La?nnec invented the stethoscope. But was he the first one? On a recent trip to Egypt we visited the temple of Kom Ombo, built prior to the roman period and renowned as a medical care center. Today, the tourist is fascinated by the magnificent hieroglyphics on the well-preserved walls testifying to significant advances in various fields of medicine including ophthalmology and gynecology. We were particularly interested by the basreliefs presenting vivid drawings of some of the first medical instruments. We easily identified curettes, scissors, a balance, forceps for dental extraction, and a surgical saw, but were captivated by two other instruments. The first one looked a lot like what La?nnec invented around 1820. The second one was amazingly similar to the instrument we use everyday, with a distal opening and flexible tubes (woven papyrus?) leading to proximal ear pieces. Our Egyptian guide was formal: the stethoscope was invented in Egypt. The scientific impact of our observations leaves something to be desired, but did make us think about the huge gap between the advancement of medical knowledge in ancient Egypt and La?nnec's (re)-invention. Exposed to a similar gap in history, what would our documents stored on CD and video tapes have to say to future touring doctors?  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号